A modern oil refinery converts crude oil through numerous unit operations and conversion reactions into several individual streams, called including diesel, jet fuel, and gasoline blendstocks that are stored in separate tanks so they can be blended together in calculated proportions to obtain various grades of “finished” gasoline that consumers purchase at the service station pump. The gasoline product is a complex blend of hydrocarbons that is subject to a variety of technical and regulatory limitations on the concentrations of certain individual chemical compounds, chemical elements, and classes of chemical components. Examples include limits on the amount of benzene allowed in finished gasoline (currently 0.62% by volume), limits on the amount of organo-sulfur compounds which are limited indirectly by a specification of the total amount of the element sulfur (currently 30 ppm), and limits on the total amounts of aromatics and olefins, either directly for reformulated gasoline or indirectly through limits calculated by the so-called “complex model” for air toxics as administered by the US EPA. There are also physical property limits to gasoline such as its Reid Vapor Pressure (RVP), and distillation mid and end points.
In the United States there are additional laws that require gasoline, jet, and diesel fuels to contain renewable-sourced blendstocks between specific minimum and maximum levels. Today those limits are set by Congress via the Renewable Fuels Standards (“RFS”). The RFS mandates that 21 billion gallons of advanced biofuels will need to be produced by 2022. A part of these advanced biofuels will be fungible transportation fuels such as gasoline, jet fuel, and diesel derived from biomass. Efforts continue on producing such fuels from biomass to meet the mandate and it is perceived that there will be a strong demand for gasoline, jet, and diesel fuels produced economically from biomass. The chief renewable-sourced gasoline blendstock used in the U.S. to meet the gasoline blending requirement is ethanol, produced largely from corn or sugar fermentation. A minor, but growing contribution to the nation's renewable gasoline pool is so-called “second generation” cellulosic ethanol made from non-food biomass such as corn stover.
There are several issues that make ethanol a less-desirable renewable gasoline blendstock. One of these is that most ethanol is produced from corn, which otherwise could be used for human or animal food. Furthermore, the land used to grow corn for ethanol production could be re-purposed to grow other kinds of food crops if other sources of renewable fuels besides ethanol could be produced. This is a societal issue that is a disadvantage for ethanol production; there are also many technical disadvantages of ethanol.
The technical disadvantages of ethanol as a fuel blendstock include the fact that ethanol is hygroscopic and therefore cannot be transported in pipelines that are used to ship conventional gasoline or other pure hydrocarbon products, otherwise water drop-out and pipeline corrosion issues may occur. This has resulted in the establishment of a separate ethanol supply chain and infrastructure, and the need for “splash blending” to make the final gasoline composition. Splash blending occurs when ethanol is added to gasoline at the gasoline distribution and tanker truck depot which makes it more difficult for refineries to optimize their intermediate “base” gasoline formulations (e.g. Reformulated Gasoline Blendstock for Oxygen Blending or “RBOB”, and Conventional Blendstock for Oxygenate Blending or “CBOB”) that become “finished” gasoline after ethanol addition. This can result in sub-optimal compositions that lead to “octane giveaway”, meaning that consumers might receive gasoline at a higher octane rating than what is stated on the service station pump label.
Further, ethanol has been shown to have a detrimental effect on certain elastomer sealing materials used in some gasoline engines and fuel systems. This problem is worse for older engines and for non-road engines such as those used for recreational vehicles such as boats and four wheelers.
Another disadvantage of ethanol as a fuel blendstock is that ethanol has lower energy density than typical gasoline components because it is a polar molecule that contains the element oxygen. Compared to gasoline, ethanol has approximately 32% lower energy density per liquid volume of product. The energy density of gasoline ranges from 112,000 to 116,000 BTU/gal (44-46 MJ/kg), whereas ethanol is 76,000 BTU/gal (30 MJ/kg).
An important technical disadvantage of ethanol is its very high blending Reid Vapor Pressure (RVP). RVP is the absolute vapor pressure exerted by a material at 100° F. (37.8° C.). Blending RVP represents the material's contribution to the RVP of a mixture such that the RVP for the mixture equals the summation of each component's blend RVP multiplied by some function of that component's volume fraction. Although pure ethanol has a relatively low RVP, the vapor pressures of ethanol-gasoline blends are higher than expected from simple mixing due to non-ideal vapor-liquid solution thermodynamics that occur because of the presence of the alcohol functional group. Ethanol has a blending RVP of more than 20 psi when blended at 10 volume percent in gasoline. It is important to note that there is no single best volatility for gasoline. Volatility must be adjusted for the altitude and seasonal temperature of the location where the gasoline will be used. To meet strict RVP limits on finished gasoline, especially for summertime blends, refiners reduce the vapor pressures of the base gasoline blends to low levels, prior to ethanol splash blending. The lower vapor pressure limit forces refiners to “back out” relatively lower value materials such as butanes, pentanes, and other hydrocarbon components from gasoline, which creates additional costs.
Because of the fundamental limitation of ethanol-containing gasoline blend vapor pressure, the U.S. EPA has relaxed the finished gasoline RVP specification for blends having 10% (volume) ethanol. These blends are allowed to have an RVP limit that is 1 psi higher than gasoline that contains no alcohol. The higher vapor pressure of the ethanol containing gasoline results in more evaporative emissions and resultant air pollution problems.
In the manufacture of ethanol by fermentation, various sources of sulfur are present including a relatively high level sulfur in the corn feedstock (e.g. up to 1200 ppm in corn versus 500 ppm in pine and hardwoods), sulfur in the fermentation yeast, and the use of several sulfur-containing acids to adjust pH, clean equipment, and remove aldehydes from CO2 (e.g. sulfuric acid, sulfamic acid, and sodium bisulfite respectively). These contribute a relatively high level of sulfur in ethanol blendstocks. Currently ASTM4806-15 is the standard regulating the specifications for fuel ethanol and it allows total sulfur content up to 30 ppm, and sulfate is limited to 4 ppm maximum. Soon the limit on sulfur permitted in gasoline sold in the United States will be reduced to 10 ppm maximum. The reduced sulfur limit will require refiners to reduce the sulfur content of their base gasolines further to accommodate the high level of sulfur in the ethanol splash blend.
Biodiesel is a fuel having a fatty acid methyl ester (Fatty Acid Methyl Ester: FAME) component obtained by methyl esterification of fats and oils derived from living things by way of various methods. However, if the additive amount of biodiesel exceeds a certain value, the amount of heat generation by the diesel engine will decrease, and it will not be possible to heat the diesel particulate filter (DPF) to high temperature and it will clog. In addition, the generation of injector deposits and combustion deposits, causes deterioration of some fuel hoses resulting in unsafe vehicle operation. High concentrations of biodiesel can cause sludge formation and oxidative degradation, which may induce clogging of the injectors, fuel filter, piping and the like, in addition to adversely affecting vehicle performance. As a result, use of biodiesel requires special allowances and frequent component replacement, and its use is limited to 5% by volume. Therefore, a renewable diesel fuel blendstock has been sought that can be blended in high concentrations and used without special considerations.
For civilian or commercial aircraft, there are two main grades of jet fuel: Jet A-1 and Jet A. Jet fuels of both grades are kerosene-type fuel and the difference between them is that Jet A-1 fulfills the freezing point requirement of maximum −47° C., whereas Jet A fulfills the freezing point requirement of maximum −40° C. There is another grade of jet fuel: Jet B for usage in a very cold climate, a wide-cut fuel covering fractions from naphtha and kerosene, which fulfills the freezing point requirement of maximum −50° C. Jet fuels generally comprise at least 50% by weight hydrocarbon compounds with from 5 to 16 carbon atoms.
Biomass pyrolysis has been developing as an alternative to ethanol for providing renewable fuels and fuel blendstocks. The product of biomass pyrolysis is a complex and unstable bio oil whose composition varies widely depending on feedstock and pyrolysis conditions, and that comprises hundreds of compounds including a plethora of oxygenates. Generally bio oil contains 20-40% by weight oxygen and a small percentage of sulfur-containing materials. Hydrotreatment of the bio oil, including hydrodeoxygenation (HDO), hydrodesulfurization (HDS), and olefin hydrogenation, is required to make the oil suitable as a blendstock or stand-alone fuel. While hydrotreating is well developed for petroleum feedstocks that contain almost no oxygen, the challenges of hydrotreating bio oil are more substantial. To date the preferred processes for hydrotreating bio oil are multi-stage systems that require high pressure of hydrogen, precious metal catalysts, and multiple unit operations (see for example, “Process Design and Economics for the Conversion of Lignocellulosic Biomass to Hydrocarbon Fuels: Fast Pyrolysis and Hydrotreating Bio-oil Pathway,” S. Jones et al, PNNL-23053, November 2013, available electronically at http://www.osti.gov/bridge).
Catalytic fast pyrolysis of biomass has been developed as an improved thermal process for upgrading biomass to chemicals and fuels. The process involves the conversion of biomass in a fluid bed reactor in the presence of a catalyst. The catalyst is usually an acidic, microporous crystalline material, usually a zeolite. The zeolite is active for the upgrading of the primary pyrolysis products of biomass decomposition, and converts them to aromatics, olefins, CO, CO2, char, coke, water, and other useful materials. The aromatics include benzene, toluene, xylenes, (collectively BTX), and naphthalene, among other aromatics. The olefins include ethylene, propylene, and lesser amounts of higher molecular weight olefins. BTX aromatics are desirable products due to their high value and ease of transport. Toluene and xylenes are particularly desirable as gasoline components due to their high octane rating and energy density. Heavier aromatics are suitable precursors to jet and diesel fuels. When produced under proper conditions, the products of catalytic fast pyrolysis are very low in oxygen content.
U.S. Pat. No. 9,062,264 discloses a process and system for producing a renewable gasoline by separating a bio-gasoline fraction from bio oil, and directly blending it with a petroleum-derived gasoline, without any prior hydrotreatment. The disclosure also describes bio-gasoline compositions derived from lignocellulosic biomass catalytically pyrolyzed in a riser reactor in which the bio-gasoline contains hydrocarbons and oxygenates wherein phenolic compounds comprise at least 10% by weight, or carbon- and oxygen-containing compounds comprise at least 15% by weight of the bio-gasoline.
U.S. Pat. Nos. 8,277,684 and 8,864,984 disclose that products from a catalytic fast pyrolysis process using zeolites such as HZSM-5 as catalyst contain aromatics, that the products have high octane and can be used directly as fuels or as fuel additives, and a method for producing a biofuel or fuel additive composition with an octane number of at least 90 from a solid hydrocarbonaceous biomass material. However, without further processing only very minute quantities of the raw product mixture can be blended into gasoline to produce a gasoline blend that meets regulatory specifications. The disclosures do not address the conditions or processes required to produce a gasoline blendstock, the amount of fuel additive that could be used in a gasoline blending base stock or in a finished gasoline composition, or the properties of such a blended fuel. The disclosures do not suggest the removal of heteroatom contaminants, such as sulfur, nitrogen, and oxygenates, how to achieve a product that meets the allowable limits of dienes, vinyl-aromatics (e.g. styrene), and olefins in the product, nor how to achieve various gasoline blend specifications. The disclosures do not suggest concepts or process configurations to produce C5/C6 naphtha, cyclohexane, linear alkyl benzenes, or naphthenes.
In U. S. Patent Publication No. 2014/0107306 A1, a method and apparatus are described for pyrolysis of biomass and conversion of at least one pyrolysis product to another chemical compound. The latter method comprises feeding a hydrocarbonaceous material to a reactor, pyrolyzing within the reactor at least a portion of the hydrocarbonaceous material under reaction conditions sufficient to produce one or more pyrolysis products, catalytically reacting at least a portion of the pyrolysis products, separating at least a portion of the hydrocarbon products, and reacting a portion of the hydrocarbon products to produce a chemical intermediate.
In U.S. Pat. Nos. 8,277,643; 8,864,984; U.S. Patent Publication 2012/0203042 A1; U. S. Patent Publication 2013/0060070 A1, U. S. Patent Publication 2014/0027265 A1; and US Patent Publication 2014/0303414 A1, each incorporated herein by reference in its entirety, apparatus and process conditions suitable for catalytic fast pyrolysis are described.
In light of current commercial practices and the disclosures of art, a simple economical process for producing renewable gasoline blending stocks, diesel fuels, or jet fuels that meet technical and regulatory limitations by use of catalytic pyrolysis of biomass is needed. The present invention provides such a process and the resulting blend compositions and chemicals.